The easiest way is to download and install Q2A Ultimate SEO plugin from GitHub.
Once installed, go to admin→plugins and enable it.
Then go to admin→Ultimate SEO and there you can customise SEO features to your liking, including changing how the homepage title is displayed on search engines and social media. You can also set default meta tags and default images to be used when your site is shared online.
Also there are many other options that you can tweak which will help your site with SEO.
The other way is to change lang files but the first option is easier.